Photocurable inks are quick to dry, contain no volatile solvents that may volatilize and have harmful effects on the environment, and can also be printed on various base materials, and for these excellent performance characteristics, they are used in wide-ranging fields such as offset printing, gravure printing, screen printing, letterpress printing, and various other coating and inkjet printing applications.
In particular, inkjet printing provides an easy, inexpensive way to create images on base materials of any material or shape, and thus is applied in a variety of fields from traditional printing of logos, graphics, photo images, etc., to marking, color filtering, and other special printing applications; when combined with the performance of photocurable inks, therefore, inkjet printing is expected to produce better printed matter.
Furthermore, there is a call, of late, for various base materials that are stretched or bent after printing, to be printable by the inkjet method.
Also, in recent years, light-emitting diodes (LEDs) are replacing mercury lamps and metal halide lamps as light sources used for photocurable inkjet printing ink compositions from the viewpoint of protecting the environment, and accordingly there is a call, from the viewpoint of production efficiency, for photocurable inkjet printing ink compositions that can be cured fully even with low LED irradiation energy (such as 100 mJ/cm2 or less in total light quantity).
To solve these problems, an active energy ray-curable ink is proposed that combines a monofunctional monomer and a polyfunctional monomer, wherein the monofunctional monomer contained therein is a (meth)acrylate having phenoxy groups, an ethylene oxide adduct, or a propylene oxide adduct thereof, etc. (refer to Patent Literature 1, for example). Certainly an active energy ray-curable ink having the aforementioned monomer composition offers good stretchability, but its curability, tackiness, post-processability and abrasion resistance are not sufficient.
In addition, a photocurable inkjet printing ink composition is proposed that comprises a photopolymerizable compound in which monofunctional monomers are contained by 85.0 to 99.9 percent by mass and a urethane oligomer having ethylene unsaturated double bonds is contained by 0.1 to 15 percent by mass, wherein the monofunctional monomers contain acryloyl morpholine and the content of acryloyl morpholine is 30 percent by mass or more relative to the total mass of the photopolymerizable compound, and wherein the monofunctional monomers include a monofunctional monomer having a heterocyclic ring and a monofunctional monomer having an alicyclic structure and the total content thereof is 50 percent by mass or more relative to the total mass of the aforementioned photopolymerizable compound (refer to Patent Literature 2, for example). Responding to the recent call for higher performance, the aforementioned ink composition offers good curability, tackiness, and adhesion, but it presents a problem in terms of bending tolerance.